Process for removal of elemental sulfur from crude petroleum oils with an aliphatic diamine and an adsorbent



United States Patent PROCESS FOR REMGVAL OF ELEMENTAL SUL- FUR FROM CRUDE PETROLEUM OILS WITH AN ALIPHATIC DIAIVHNE AND AN ADSORBENT Roderick S. Spindt, Allison Park, and James Harold Wright, Verona, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Application March 28, 1955 Serial No. 497,456

13 Claims. 01. 196-24) This invention relates to a process for removing elemental sulfur from crude petroleum oils.

Elemental sulfur has been found to exist in many crude petroleum oils. Although not all crude petroleum oils contain elemental sulfur, some crudes have been found to contain more than 1 percent by weight.

The presence of elemental sulfur in crude petroleum oils is highly objectionable. One objection is its highly corrosive action on various metals, leading to corrosion of pipe lines, storage vessels, and distillation facilities in general. Another objection to this type of sulfur is that it can be the source of malodorous and otherwise undesirable sulfur compounds. These undesired sulfur compounds may be formed upon distillation, cracking and other similar crude processing requiring heat, during which the elemental sulfur readily reacts with petroleum, hydrocarbons to yield objectionable sulfur compounds.

We have now found that we can remove elemental sulfur from crude petroleum oils or non-distillate fractions thereof by contacting the oil with an aliphatic diamine containing up to carbon atoms. We have thus been able to obtain such oils substantially free of elemental sulfur by the process of our invention.

The aliphatic diamines employed in the process of our invention are diamines containing up to 5 carbon atoms, and may be straight chain or branched. The preferred class of diamines comprises primary, aliphatic diamines, and simple derivatives of these, such as ethylene diamine, 1,2-diamino propane, trimethylene diamine, 1,3-diamino propanol-Z, etc.

The aliphatic diamines of our invention are liquids or very low melting solids and are completely soluble in water. These compounds are characterized by their ability to form complexes with elemental sulfur, and are miscible with crude petroleum oils. Upon contacting a crude petroleum containing elemental sulfur, the aliphatic diamines react readily with the elemental sulfur at ambient temperatures and pressures and combine with substantially all of it to form a diamine-sulfur complex. The complex is soluble in the crude petroleum and remains miscible therewith. Upon extraction of the diamine-sulfur complex with a suitable solvent, substantially all the elemental sulfur originally present in the crude petroleum is removed.

In the actual practice of one embodiment of our invention, elemental sulfur is removed from a crude petroleum oil by first contacting the oil with a sufficient amount of an aliphatic diamine containing up to 5 carbon atoms to form a diamine-sulfur complex with substantially all of the elemental sulfur present. The aliphatic diamines are employed as such or in the form of aqueous solutions. The diamine treated petroleum oil, containing in solution the diamine-sulfur complex, is then washed with a solvent which is immiscible with the petroleum oil but which dissolves the diamine-sulfur complex. An excellent solvent for this purpose is water, but other aqueous solutions such as aqueous waste refinery streams can be employed. The diamine-sulfur complex is thus removed from the oil, leaving a crude petroleum containing substantially no elemental sulfur.

In another aspect of our invention, the aliphatic diamine is employed in the form of an aqueous solution containing an amount of water at least equal in volume to the volume of crude oil being treated. When using this embodiment of our process in removing elemental sulfur from crude petroleum oils, such aqueous diamine solutions extract the elemental sulfur from the oil and two readily separable phases are formed: an aqueous phase rich in diamine-sulfur complex, and an oil phase immiscible with the aqueous phase and substantially free of elemental sulfur and sulfur-amine complex. Separation of the two phases yields a crude petroleum oil from which substantially all of the elemental sulfur has been removed.

Regardless of whether a substantially non-aqueous diamine or an aqueous diamine solution is employed, a sufficient amount of the diamine is used to combine with substantially all of the elemental sulfur present in the crude petroleum oil, preferably on the order of one mol of amine to two atoms of elemental sulfur in the oil. Thus, with ethylene diamine, for each percent of elemental sulfur present in the crude oil, an equivalent percentage by weight of the diamine is employed as the treating agent. With other diamines of greater molecular weight, correspondingly larger amounts of the diamines are ordinarily employed. However, in order to avoid losses which may occur in treating, larger amounts of the diamine can be employed, for example, from a slight excess to as much as 5 mols of diamine per atom of elemental sulfur, the upper limit being dictated by considerations of cost. Smaller amounts of the diamine than one mol' for every two atoms of elemental sulfur can also be employed, it being understood that the efliciency of the sulfur removal is thereby reduced. From the above considerations, one skilled in the art can readily determine the specific amounts of diamine necessary for treating any crude petroleum oil containing specific amounts of elemental sulfur.

Where aqueous solutions of the diamine are employed to yield immiscible phases, i. e., an oil phase substantial- I 1y free of elemental sulfur and an aqueous phase containing diamine-sulfur complex, sutficient water is employed with the diamine to yield significant amounts of an aqueous phase while leaving substantially no diaminesulfur complex in the oil phase. When the amount of water present in the aqueous diamine treating solution is at least about equivalent in volume to the volume of crude oil being contacted, the two phases formed separate readily without substantial emulsification. When the amount of water present in the aqueous diamine solution is less than the volume of crude oil being contacted, the two phases are in the form of a rather stable emulsion. Such emulsions are broken upon long standing or by the addition of emulsion breaking agents or by centrifuging. The emulsions can also be broken by adding an amount of water sufiicient to make the volume thereof at least equivalent to the volume of crude oil in the emulsion. The separated crude oil can then be washed with additional water to remove traces of diamine and/ or diaminesulfur complex.

Where aqueous solutions of the diamine are employed to obtain two phases, in general, at least about 25 percent of water should be present in the aqueous diamine solutions in order to obtain the desired two phases. We have employed with good results aqueous solutions of .diamine containing from 25 percent to percent by volume of water. It is to be noted that the efiiciency of sulfur removal is reduced by increasing amounts of water in the treating agent. Thus, while amounts of 75 percent by volume of water in the diamine-water treating agent have been found to be satisfactory, larger amounts of water are deleterious from the standpoint of reducing the amount of elemental surfur effectively removed from the oil.

When aqueous solutions of the diamines are employed as treating agents in accordance with our invention, contact of the treating agent with the crude petroleum oil can take place in batchwise fashion or in continuous countercurrent contact apparatus, such as used for example in liquid-liquid extraction processes. Similarly, the separation of the aqueous and oil phases can be accomplished batchwise, simply by settling, or continuously, as by employing centrifugal separators or time settling tanks. It is sometimes desirable to employ water washing of the separated oil phase after treatment thereof with aqueous solutions of the diamines. This is to insure removal of substantially all diamine-sulfur complex from the oil phase.

In another embodiment of our invention, a crude petroleum oil containing elemental sulfur is contacted with a suitable amount of a non-aqueous diamine, and the treated oil is percolated through a bed of solid adsorbent, such as silica gel, alumina, bauxite, fullers earth, etc. The adsorbent adsorbs substantially all of the diamiue-sulfur complex and there is obtained as a percolate a crude oil substantially free of elemental sulfur. To regenerate the adsorbent bed, the sulfur can be removed from the adsorbed diamine-sulfur complex by washing with a suitable solvent, for example, hot xylene at a temperature of from 70 to 100 C., and the diamine then recovered from the adsorbent bed by washing with water. The diamine can be recovered from the water for reuse, and the adsorbent bed can be employed for treatment of further quantities of crude oil.

Significant advantages of the process of our invention are. (l) the aliphatic diamines efiiciently remove elemental sulfur at ordinary ambient temperatures and pressures, and (2) the reaction with elemental sulfur is substantially instantaneous. Accordingly, ordinary refinery contacting apparatus can be used in the process of our invention, and the streams of crude petroleum can be processed as they arrive from pipe lines or storage tanks without any special treatment. If desired, however, the temperature of treatment of crude petroleum oils with the aliphatic diamines can be varied, for example, with ethylene diamine from about 50 F. to about 230 F. The time of treatment can also be varied, if desired.

After treatment of a crude petroleum containing elemental sulfur with an aliphatic diamine, the separated aliphatic diamine-sulfur complex can he further treated, if desired, to regenerate the diamine for reuse. The aliphatic diamine can be regenerated from its complex, for example, by stripping the sulfur-rich diamine complex with steam or other inert gas to take the diamine overhead and to leave the sulfur as a residue.

The following specific examples are further illustrative of our invention and demonstrate the effectiveness thereof in removing elemental sulfur.

Example I The eflicacy of the diamines of the invention for the removal of elemental sulfur from a crude oil was demonstrated in the laboratory as follows: Equal volumes of ethylene diamine and a McElroy crude oil containing 0.47 percent by weight of elemental sulfur were agitated at room temperature for approximately 5 minutes. The two liquids were completely miscible. After standing for some time, the mixture was washed with several volumes of water to remove the ethylene diamine-sulfur complex from the oil. The oil was then analyzed and the results were compared with the original sample.

Several samples of another McElroy crude oil were treated with aliphatic diamines under the conditions set forth in Example I, except that 0.4 volume of the diamine was employed per volume of oil. The reduction in elemental sulfur content obtained is shown in the following table:

Total Elemental Percent Diamlne Sulfur, Sulfur, Elemental Percent Percent Sulfur by Wt. by Wt. Removed None (untreated crude) 2. 34 0. 541 Ethylene dlamlne 1. 70 0. 004 99+ 1,2-Dlamlno propane. 1. 94 0. 114 79 1,3-Dlamino propanol-2 2.08 0. 249 54 Example III In this example, there is shown the effectiveness of aqueous solutions of the aliphatic diamines as treating agents, the solutions containing 25, 50 and percent by volume of water, respectively. In each instance, the diamine solution was added to the crude oil sample at room temperature, the mixture was then agitated for 2 minutes and the oil was finally washed with 20 volumes of water to remove any remaining ethylene diaminesulfur complex.- The treated crude oil samples were then centrifuged to remove any traces of water. The following table shows the results obtained. Ethylene diamine containing no water is included for purposes of comparison.

In the above examples, the amount of elemental sulfur present in the oils was determined by the polarographic method. This method is described in detail in an article entitled Elemental Sulfur in Crude Oils by Eccleston, Morrison and Smith, Analytical Chemistry, vol. 24, November 1952, at pp. 1745 et seq.

Examples I, II, and III above demonstrate the effectiveness of the aliphatic diamines in removing elemental sulfur from crude petroleum. In each example the amount of elemental sulfur removed ranged from over 50 percent to almost 100 percent. Ethylene diamine, as shown in Examples I and II removed almost 100 percent of the elemental sulfur in each case, and for this reason constitutes the preferred diamine. It is to be noted, furthermore, that in each example the reduction in total sulfur content was almost completely due to the elemental sulfur removed. Example III shows the effectiveness of aqueous solutions of ethylene diamine. Thus, solutions of ethylene diamine and water in a 50:50 proportion are capable of removing over percent of the elemental sulfur present in the crude petroleum.

This example shows the process of our invention as adapted to a continuous treatment of a crude petroleum oil containing elemental sulfur. A crude petroleum oil containing about 0.5 percent by weight of elemental sulfur is charged to the bottom of a conventional continuous countercurrent extraction tower at the rate of 500 barrels per hour. Simultaneously an aqueous ethylene diamine solution containing 50 percent by volume of water is charged to the top of the tower at a rate of 2,000 barrels per hour. The crude oil and treating Solution are at a temperature at which they are withdrawn from storage or make-up, i. e., at ambient temperature. The treated crude oil is withdrawn from the top of the tower and is then washed with water at the rate of one to two gallons per barrel of treated crude in order to remove any small amounts of ethylene diamine-sulfur complex remaining in the treated oil. The spent ethylene diamine solution containing the diamine-sulfur complex is withdrawn from the bottom of the tower and regenerated by heating with steam, the stripped ethylene diamine passing overhead and then cooled, condensed and recycled after suitable adjustment of the water concentration.

Example V This example further shows our invention as adapted to a percolation process. To a crude petroleum oil containing about 0.5 percent by weight of elemental sulfur, there is added about 1 /2 quarts of ethylene diamine per barrel of crude and the treated oil is charged to the top of a tower containing as an adsorbent bed silica gel. The tower contains about 0.2 cubic foot of silica gel adsorbent per barrel of crude to be treated. The treated crude oil is percolated through the bed to obtain a percolate containing substantially no elemental sulfur, while the adsorbent bed absorbs substantially all the ethylene diamine-sulfur complex. By employing two or more adsorbent towers, the elemental sulfur and the ethylene diamine can be recovered from the diamine-sulfur complex adsorbed on one of the beds, while the other bed is being used in the treating process. The sulfur is first removed by percolating through the used bed about 3 /2 gallons of xylene at a temperature of 90 to 95 C. per barrel of crude treated. The sulfur can be recovered from its xylene solution by any conventional method. The ethylene diamine is recovered next by percolating from 1 to 2 gallons of water per barrel of oil treated through the bed. The aqueous ethylene diamine recovered as percolate can be led to apparatus to separate the water therefrom, and the diamine can then be recycled to treat more crude oil.

The effectiveness of the aliphatic diamines as corrosion inhibitors when added to crude petroleum oils containing elemental sulfur is demonstrated in the following example.

Example VI To four samples of a McElroy crude oil containing approximately 0.51 percent by weight of elemental sulfur there were added varying amounts, ranging from 0.5 to percent by weight of ethylene diamine. The reduction in corrosion was determined by the well known copper strip test (ASTM, D130-50T). Briefly, the copper strip test involves the immersion of a polished copper strip in a sample of the oil being tested followed by heating the sample at 122 F. for a period of 3 hours. At the end of the test the copper strip is removed and compared with reference strips. The tested strip is rated according to its appearance with a number 0, 1, 2, 3, 4 or 4+ for various degrees of corrosion. The foregoing numbers correspond respectively to no tarnish, slight tarnish, moderate tarnish, dark tarnish, slight corrosion and pronounced corrosion. The results of this test were as follows:

Copper Strip Ethylene Diamiue, Percent by Wt. N 0. (3 Hrs None (untreated crude) 4+ 0.5- 4+ 1+ 4+ 4+ Examination of the copper strip immersed in the crude oil containing no ethylene diamine indicated pitting and discoloration due to heavy sulfide formation. This discoloration and sulfide formation was due to the corrosive, elemental sulfur in the crude petroleum. With the ethylene diamine treated samples, however, the copper strips were found to be simply coated with a thin film of asphaltic material. These copper strips were washed with benzene and the asphaltic material was removed. The exposed copper from these latter strips showed no evidence of corrosion, despite the apparent discoloration noted upon initial examination.

The invention also can be applied as follows. To a crude petroleum being transported via pipe line there can be added minor amounts of an aliphatic diamine to reduce corrosion of the pipe line during transport of the oil, and thereafter, the diamine-sulfur complex formed can be removed from the treated oil at the terminal or other suitable point to yield a crude oil containing no elemental sulfur. For example, a crude petroleum containing approximately 0.5 percent by weight of elemental sulfur can be treated with about 1 /2 quarts of ethylene diamine per barrel of crude oil prior to transportation. At the terminal or refinery, the ethylene diamine-sulfur complex can be removed from the crude by any of the processes disclosed hereinabove, thereby providing a crude containing substantially no elemental sulfur.

We may also advantageously treat corrosive crude containing elemental sulfur at the production stage. Thus, in wells producing crude petroleum containing ele mental sulfur, ethylene diamine can be injected in the well annulus to protect the casing, tubing and other metal parts from corrosive sulfur. The produced treated crude can then be transported by pipe lines or the ethylene diamine-sulfur complex can be removed, as described above.

Although we have primarily described our invention in relation to the treatment of crude petroleum oils containing elemental sulfur, it is within the scope of the invention to treat an elemental sulfur-containing nondistillate fraction of a crude petroleum oil, for example as is obtained by such processes as chromatographic fractionation, thermal diffusion and the like, in which processes the heating of the crude petroleum oil is insufiicient to cause reaction of the elemental sulfur with petroleum hydrocarbons. The benefits of the invention are also obtained in the treatment of such non-distillate fractions.

Our invention provides an effective method for the control and removal of sulfur, determinable as elemental sulfur, from crude petroleum oils and the non-distillate fractions thereof described above. The removal of such corrosive sulfur leads to advantages in the handling and further processing in that corrosion of equipment due to elemental sulfur is substantially eliminated. Maintenance costs are therefore considerably reduced.

Resort may be had to such modifications and variations as fall within the spirit of the invention and the scope of the appended claims.

We claim:

1. In the treatment of a crude petroleum oil or a non-distillate fraction thereof containing elemental sulfur, the method which comprises contacting said oil with an aliphatic diamine containing up to 5 carbon atoms to form a complex of said sulfur and said diamine and thereafter removing the said complex from said oil.

2. A process for removing elemental sulfur from a crude petroleum oil which comprises adding to said oil an aliphatic diamine containing up to carbon atoms to form a complex of said sulfur and. said diamine, and thereafter removing the said complex from said oil.

3. The process of claim 2, wherein said diamine is ethylene diamine.

4. The process of claim 2, wherein said diamine is 1,2- diarnino propane.

5. The process of claim 2, wherein said diamine is 1,3-diamino propanol.

6. The process of claim 2, wherein said complex is removed by extraction thereof with water. 1

7. The process of claim 2, wherein said complex is removed by percolation through a bed of solid adsorbent.

8. A process for removing elemental sulfur from a crude petroleum oil which comprises contacting said oil with an aqueous solution of an aliphatic diamine containing up to 5 carbon atoms, said solution containing sufficient water to form a separate aqueous phase, and separating said aqueous phase containing a complex of said sulfur and said diamine from an oil phase of re duced elemental sulfur content.

9. The process of claim 8, wherein the diamine is ethylene diamine and the water content of the aqueous solution thereof ranges from 25 to 75 percent by volume.

10. The process of claim 8, wherein the aqueous diamine solution contains an amount of water at least equal in volume to the volume of crude oil being treated.

11. A process for removing elemental sulfur from a crude petroleum oil which comprises contacting said oil with an ethylene diamine in an amount sufficient to form a diamine-sulfur complex, percolating said contacted oil through a bed of solid adsorbent to obtain a crude oil percolate substantially free of elemental sulfur, washing said bed with an elemental sulfur solvent to remove elemental sulfur from the diamine-sulfur complex, then washing said bed withv water to obtain an aqueous solution of the diamine, and separately recovering the elemental sulfur and diamine from their respective solutions.

12. The process of claim 11, wherein the ethylene diamine is recycled for treatment of additional crude 'oil, and the adsorbent bed after removal of elemental sulfur and diamine is employed again for percolation of contacted oil.

13. The process of claim 12, wherein there are provided at least two adsorbent beds, at least one of which is on-stream for percolation of contacted crude oil, and at least another of which is being regenerated by removal of elemental sulfur and ethylene diamine.

References Cited in the file of this patent UNITED STATES PATENTS 2,069,329 Roelfsema Feb. 2, 1937 2,287,118 Mottlav June 23, 1942 2,393,212 Young et al. Jan. 15, 1946 2,538,066 Walsh et a1. Jan; 16, 1951 2,602,044 Lupfer etal. July 1, 1952 

11. A PROCESS FOR REMOVING ELEMENTAL SULFUR FROM A CRUDE PETROLEUM OIL WHICH COMPRISES CONTACTING SAID OIL WITH AN ETHYLENE DIAMINE IN AN AMOUNT SUFFICIENT TO FORM A DIAMINE-SULFUR COMPLEX, PERCOLATING SAID CONTACTED OIL THROUGH A BED OF SOLID ADSOEBENT TO OBTAIN A CRUDE OIL PERCOLATE SUBSTANTIALLY FREE OF ELEMENTAL SULFUR, WASHING SAID BED WITH AN ELEMENTAL SULFUR SOLVENT TO REMOVE ELEMENTAL SULFUR FROM THE DIAMINE-COMPLEX, THEN WASHING SAID BED WITH WATE TO OBTAIN AN AQUEOUS SOLUTION OF THE DIAMINE, AND SEPARATELY RECOVERING THE ELEMENTAL SULFUR AND DIAMINE FROM THEIR RESPECTIVE SOLUTIONS. 